Many employees justify their cyberloafing behavior as a mental break that can replenish their attentional resources. However, there is little empirical research to examine the effect of cyberloafing on employee attentional state. We conducted an EEG-based lab experiment to investigate the effects of two types cyberloafing activities as a mental break (i.e., watching short funny videos and browsing online news) and an offline mental break (i.e., sitting quietly and resting) on individual attentional state (including attention reengagement, attention concentration, and attention sustainability). Our findings show that, compared with browsing online news and quiet sitting, watching short funny videos as a mental break can result in a difficulty of attention reengagement, but a higher level of attention concentration and attention sustainability. The findings of our experiment indicate that the choice of mental break should be tailored to the specific type of work task at hand.